MARTETIC technical guide
Geotechnical study for screw piles: what information it must provide
The fact that the foundation is installed without digging trenches does not reduce the importance of the ground. An essential part of the system remains invisible after installation.
Direct answer
The geotechnical study provides information about the foundation ground for the building project. For a screw foundation, this data helps assess the stratification, water, risks and working conditions. It is correlated with the loads, the characteristics of the products and the checks provided for by the designer.
Is it necessary even when the foundation is on screws?
For building documentation, geotechnical requirements are set according to the framework applicable to the project. NP 074-2022 treats geotechnical documentation as a component of the project and distinguishes the geotechnical study, the geotechnical design and the other documentation.
Choosing a screw foundation does not, in itself, constitute an exception to the design requirements. Ask the designer and the geotechnical engineer to determine the documentation and investigations needed for your work. A visual assessment at quoting stage must not be presented as a geotechnical study.
Reference: NP 074-2022, chapters 1 and 2, text published in the Official Gazette (Monitorul Oficial), approved by Order no. 27/2023.
What you tell the geotechnical engineer when you request the study
Describe the building and the fact that you are analysing a screw foundation. Send the site plan, the dimensions, the height regime and the available structural information. If you have positioning options on the plot, show them before the investigations are set.
Specify the known history: fill, demolished buildings, backfilled trenches, areas with water or recent interventions. An old photograph of the plot can help formulate the right questions.
The number, type and depth of the investigations are not chosen by a universal commercial rule. They must respond to the building and the risks of the site.
What information is useful for analysing the foundation
| Information | Question to clarify |
|---|---|
| Stratification and fill | What materials does the screw pass through and where can the proposed configuration work? |
| Geotechnical parameters | Is the data needed to check resistance and displacements available? |
| Groundwater and relevant variations | What effects must be considered in design and execution? |
| Behaviour on wetting, freezing or volume changes | What local conditions can change the behaviour of the foundation? |
| Aggressiveness of the environment, when relevant | What information is needed to assess protection and durability? |
| Slope and neighbouring properties | Are additional checks of stability or interaction with existing works needed? |
The list is a discussion topic for the design team. It is not a universal specification for investigations and does not assume that every project requires the same tests.
Why a conventional pressure does not automatically mean a screw's capacity
A study written for another foundation solution may include values and recommendations for shallow foundations. These do not transfer automatically to a screw through a simple multiplication by the area of the flange or the thread.
The designer must use a method suited to the system, relevant geotechnical data and the product documentation. The check also includes the resistance of the steel element, the connections and the acceptable displacements.
If the existing study does not contain enough data for the chosen solution, ask for a supplement formulated by the project's specialists. More useful than a calculation started from an isolated value is to identify exactly the missing information.
How the study helps in choosing the length
Comparing a 1,500 mm screw with a 2,000 mm one only makes sense together with the installation level and the stratification. The total length of the product is not the same as the length remaining in the ground.
On the same site there can be different levels, uneven fill or the need for modular components. Choosing a greater length must have a justification and remain compatible with the installation and the product.
A catalogue diameter, taken on its own, does not say how many tonnes a point can support on your plot. For the final selection, the assembly of product, ground and load is checked.
The study and on-site testing complement each other
A load test follows the response of one point under certain conditions. The study provides the geotechnical context in which the result must be interpreted. A successful test does not automatically describe all areas of a property.
The test programme must specify the points, the loads, the load steps, the measurement of displacements and the acceptance criteria. These are set for the project, before the results are interpreted.
The pressure in the hydraulic system, the installation torque and the force measured in a test are different quantities. They are not converted into one another without a justified method and adequate data. More information about execution checks is in the MARTETIC installation guide.
How to send the study for analysis
Send the complete document, with the annexes, the position of the investigations and the results available. A photograph of only the conclusions page can hide application conditions or information about the variation of the layers.
Add the building plan and indicate its location relative to the investigated points. If the geometry or position has changed since the study was drawn up, mention it.
A neighbour's study can provide context, but it is not automatically considered representative of your plot and project. The use of existing investigations must be assessed by the geotechnical engineer.
Frequently asked questions
Can the installer replace the study with a trial screw-in?
A trial can provide information about installation. It does not automatically replace the geotechnical documentation and the checks required by the project.
Does the study show every stone in the ground?
No. The investigations describe the conditions at the points and by the methods used. Local obstacles may remain unidentified between them.
If the study recommends concrete, are screws excluded?
The recommendation must be discussed with the geotechnical engineer and the designer. Another solution may need additional data and checks, and at some sites it may be unsuitable.
Can I get an estimate without a geotechnical study?
A preliminary budget with explicit assumptions can be discussed. Confirmation of the solution and the execution needs the data and documentation set for the project.
Do screw pile foundations need a geotechnical study?
Choosing a screw foundation does not, in itself, constitute an exception to the design requirements. Ask the designer and the geotechnical engineer to determine the documentation and investigations needed for your work.
Is a visual site assessment the same as a geotechnical study?
No. A visual assessment at quoting stage must not be presented as a geotechnical study.
Do you already have the geotechnical study?
Send the complete document together with the building plan and the locality. If the study has not been done, specify the project stage in order to clarify the necessary steps.
The information explains how a project is prepared and is not an execution plan. The solution is determined for the real building and site, on the basis of the applicable documentation and the project's checks.